A major obstacle to the successful treatment of aculte leukemia is the lack of a sensitive in vitro assay of residual leukemia cells after morphologic remission has been achieved. Using a short-term in vitro culture of leukemia marrow, we have made preliminary observations on colony-stimulating-factor (CSF) concentration. This assay appears to be sensitive and more quantitative than previously reported in vitro tests of granulopoiesis and may reflect residual leukemia mass when applied serially to patients under treatment for leukemia. Marrow cells obtained from patients with acute leukemia at various stages of treatment and from normal controls are plated in a methylcellulose medium with varying concentrations of CSF. Colony growth, marrow cell proliferation and (3H)-thymidine uptake are determined concomitantly as a function of CSF concentration on day 14 of culture. Similar determinations are made at frequent intervals in culture to assess the kinetics of colony growth, marrow cell proliferation and (3H)-thymidine uptake. This system assesses not only colony growth but also responsiveness of marrow cells to increasing amounts of growth stimulation by CSF. When compared to normal marrows, subtle abnormalities in granulopoiesis can be detected in remission leukemia marrow perhaps indicative of residual leukemia. The objective of this research proposal are to apply this new in vitro analysis of marrow growth to studies of the effect of leukemia cells on normal granulopoiesis using an autologous coculture system; determine whether abnormalities in the culture system reflect occult leukemia cells in remisssion leukemia marrow; determined if the pattern of leukemia marrow at diagnosis correlates with remission induction.